Various possibilities for altering the stress or tension distribution in metal strip have been described in the literature. One such practical technique utilizes stretch bend leveling in which the continuously travelling metal strip is subjected to plastic deformation in the longitudinal and transverse direction by passing it through an array of rollers which are so oriented that the strip is bent in one direction and in opposite direction as it passes through the roller array.
Transverse curvature can be eliminated or ameliorated and metal strip which could be considered out of level can be leveled, i.e. made planar.
In stretch bend leveling, the stretch bend leveling rolls are pressed to a lesser or greater degree into the plane of travel of the metal strip. The tension applied in stretch bend leveling can be adjusted, for example, by the depth of penetration of the stretch bend rollers into the path.
The problem with stretch bend leveling, of course, is that the stretch bend rollers are always in contact with the opposite surfaces of the metal strip and this contact can have a detrimental affect on the surface quality of the product. For example, it cannot be excluded in the course of stretch bend leveling that dirt and contaminants can pass between the stretch bend rollers and the surface treated and can be pressed into the surface of the strip and thereby contribute an undesirable roughening thereto. Furthermore, a highly sensitive and accurate adjustment of the stress distribution is expensive with the stretch bend leveling system.
A stress distribution control system utilizing linear motors is described, for example, in the Soviet publication SU 1585040-A. The stress distribution is controlled, in this system, for a continuously travelling metal strip, by means of three linear motors. How the stress distribution of the travelling strip is detected, however, is not described in detail here nor is a reaction to different types of stress distribution possible with this system.
The same applies to the control purposes described in JP 62-130961A for influencing the stress in a metal strip. Linear motors are here provided on both sides of the metal strip which is maintained under tension between tension rollers. The strip travel is stabilized with this system.
To generate transverse movements with respect to the continuously travelling metal strip, linear motors are described in the Japanese Patent Document JP 62-130959. The goal with this system is to largely eliminate or reduce the meandering of the continuously travelling strip and thus to suppress transverse curvature.